Integrated circuit semiconductor devices are fabricated in multiple arrays from thin slices or "wafers" of semiconductor material. such processing generally begins with the fabrication of a thin polished slice of a single crystal material formed by slicing across a single crystal ingot which may have a diameter of about one inch or more. The polished slice is then subjected to a succession of photoresist masking, impurity diffusion, and metal depositation operations to form an array of semiconductor devices which may range from several hundred to several thousand, depending upon the size and complexity of the integrated circuit. Each of these operations is generally performed in a different location with different equipment. As the wafers are generally held in cassettes for processing, the wafers must be passed through the various machines, from one cassette to another during the fabrication process.
Many different devices have been proposed to transport the wafers, but all generally have certain disadvantages. For example, many of the electromechanical transportation systems currently in use require electrical connections to the portion of the mechanism which moves the wafer. The common type of wafer transfer mechanism has the problem of friction contamination because of the contact of various mechanical parts which produces a fine dust contaminating both the clean rooms in which the wafers are produced, as well as the wafers themselves. Likewise, because of the precise positioning requirements demanded in integrated circuit fabrication, many of the devices currently used are complicated electromechanically in order to achieve the desired positioning accuracy. An additional problem has been the difficulty in moving the semiconductor wafer from one transportation mechanism to another, as is required, for example, when wafers are moved through vacuum valves which appear at the entrances of many of the machines utilized in integrated circuit fabrication.
Accordingly, it is the principal object of the present invention to move semiconductor wafers in a simple and efficient manner through the various machines used in integrated circuit fabrication, process and inspection.
It is a further object of the present invention to facilitate the automatic transfer of semiconductor wafers between integrated circuit processing machines.
Yet another object of the present invention is to accurately position a semiconductor wafer for processing.